In recent years, the market for memory cards incorporating nonvolatile memories, as storage media in digital cameras and cell phones, has been expanding. And the capacity of NAND flash memories, which are nonvolatile memories used in memory cards, has been increasing as miniaturization of semiconductor fabrication processes has been advanced.
Along with this capacity increase, the amount of files recordable into a memory card has been increasing. Therefore, memory cards are being used for digital movies as well, for which memory cards have not been used before, and large files, such as moving image files, are recorded in memory cards. When a moving image file of a movie is being recorded, it is necessary to take moving images while recording the images in the memory card. Thus, although the moving image file is a single file, writing is performed multiple times at fixed time intervals to write the file of large size.
Also, as the capacity of nonvolatile memories has been increased, the capacity of physical blocks, which are erase units, in NAND flash memories has been increased.
However, the increase in the size of written files and the increase in block capacity in NAND flash memories are events independent of each other, and thus cause degradation in performance in writing to memory cards. Patent Document 1 discloses factors of such performance degradation and a method for avoiding such performance degradation.
Furthermore, as the capacity of cards increases, it will become possible to store various kinds of information in a single memory card, consequently enabling the use of the memory card in a system in which different types of files are written in parallel. For example, a system is possible in which while a moving image file is recorded and audio in a different file is also recorded, still images can be recorded at any timing desired by the user. In another possible system, moving image files from multiple surveillance cameras can be written into multiple files in parallel. In these systems, the host equipment, which is equipment for writing data into the memory card, just writes data having logical meanings (i.e., types) in parallel, but, in the memory card, multiple files are randomly written in a mixed manner. With the solution disclosed in Patent Document 1, the performance of these systems cannot be maintained.    Patent Document 1: Japanese Laid-Open Publication No. 2002-366423    Patent Document 2: Japanese Laid-Open Publication No. 9-128155    Patent Document 3: Japanese Laid-Open Publication No. 2001-325128    Patent Document 4: Japanese Laid-Open Publication No. 2006-65505    Patent Document 5: International Publication WO 2005/106673